The present invention relates to a method of preparing 4-disubstituted phenyl-1-tetralones, also called 4-disubstituted phenyl-3,4-dihydro-1-(2H) naphthalenones and more precisely 4-disubstituted phenyl-1-tetralones of formula ##STR3## in which X represents a halogen atom, a C.sub.1 -C.sub.4 alkyl group or a C.sub.1 -C.sub.4 alkoxy group and
Y is situated in position 2' or 3' and represents a halogen atom or a C.sub.1 -C.sub.4 alkyl group. PA0 Y is situated in the ortho or meta position with respect to X and represents a halogen atom or a C.sub.1 -C.sub.4 alkyl group.
These tetralones are known for being particularly useful as synthesis intermediates for preparing different serotonine pre-synaptic inhibitor compounds with anti-depressive property, described more particularly in the U.S. Pat. Nos. 4,029,731 and 4,045,488 and the European patent No. 0 030 081.
Up to the present time, the tetralones of formula (I) have been prepared using a method comprising five steps described in Organic Reaction, vol VI, pages 1 to 73 and in the above mentioned European patent. This known method comprises (a) the reaction of benzoyl chloride with an aromatic hydrocarbon in the presence of aluminium chloride, which leads to benzophenones, (b) condensation of the latter, under the conditions of Stobbe's reaction in the presence of a strong base such as potassium tertiobutoxide, with diethyl succinate, (c) decarboxylation of the compounds obtained, using an aqueous hydrobromic acid solution, which leads to 4,4-diaryl butenoic acids, (d) hydrogenation of the latter on palladium charcoal in 4,4-diaryl butanoic acids, and (e) cyclization of the latter in 4-aryl tetralones, either directly by means of hydrofluoric acid or polyphosphoric acid, or, after transformation into acid chlorides using thionyl chloride, by the action of aluminium chloride under the conditions of Friedel-Crafts reaction.
This known method has different drawbacks. In fact, it is extremely long since it comprises five steps which each require a relatively long reaction time. Moreover, it uses expensive reagents such as potassium tertiobutoxide and palladium charcoal, or aggressive agents and so dangerous to use such as hydrobromic acid, hydrofluoric acid and thionyl chloride. Furthermore, because of the large number of steps required, the overall tetralone yield is very low since, in the best of cases, it does not exceed 40% with respect to the benzoyl chloride.
All these drawbacks undeniably form major obstacles to the industrial use of the method in question.